The invention relates to a method for a synchronized ignition in an internal-combustion engine with a crankshaft sensor and a device for detecting smooth running.
In the case of a four-stroke engine, the operating cycle comprises the intake, the compression, the working and the discharge operations, in which case each cylinder moves up and down twice and in this case comes to a stop in two upper (top) dead centers (OT) and two lower dead centers (UT). Thus, during one operating cycle, the crankshaft carries out two rotations; the camshaft carries out one rotation. The ignition of the gas-fuel mixture charged in a cylinder takes place at an upper dead center in which the mixture has just been compressed. This is the ignition upper dead center (ZOT). In contrast, there is also an overlapping upper dead center (xc3x9cTO) in which, during the transition from the discharge to the intake, the inlet as well as the outlet valves are opened.
When a crankshaft sensor is used, it can be determined when an upper dead center is present. However, it cannot easily be determined whether this is the ignition upper dead center or the overlapping upper dead center. For differentiating between these upper dead centers, a camshaft sensor is conventionally used which indicates the ignition upper dead center.
Without such a camshaft sensor, ignitions had to be implemented in the ignition upper dead center as well as in the overlapping upper dead center. Furthermore, without a precise differentiation between the ignition upper dead center and the overlapping upper dead center, no fully sequential cylinder injection can be implemented.
From German Patent Document DE 41 22 786 A1, a method is known for the identification of the angle of rotation of an internal-combustion engine assigned to an ignition or injection operation. According to an embodiment, for starting the engine, an ignition operation is first initiated each time the angle of rotation is reached. After the start, such an ignition operation is initiated only at each second reaching of the angle of rotation, a conclusion being drawn on the crank angle from the comparison of an actual reaction and a desired reaction. In this case, it is a disadvantage that unburnt fuel/air mixture can reach a catalyst on the output side and can burn there.
Disadvantages of an ignition at both upper dead centers a less smooth running, a higher consumption, higher emissions, a more extensive spark plug wear and a so-called xe2x80x9cexhaust backfirexe2x80x9d.
In contrast, when a separate camshaft sensor is used, additional costs are required for the sensor or the sensor wheel and the additional periphery.
It is an object of the invention to provide a method for a synchronized ignition in which the ignition upper dead enter can be determined without a camshaft sensor.
This object is achieved by a method for a synchronized ignition in an internal-combustion engine having a crankshaft sensor as well as a device for detecting smooth running, characterized in that, (a) after the start of the vehicle, an ignition takes place at least in one cylinder in all upper dead centers (OTs), a shifting of the ignition point in time taking place by a defined value in certain upper dead centers; (b) the effect of the ignition point in time adjustment is detected by way of the detection of the smooth running; and (c) an ignition upper dead center is assumed in the upper dead center in which the shift of the ignition point of time is taking place if the running smoothness changes above a defined limit value, and an ignition upper dead center is assumed in the upper dead center in which no shift of the ignition point in time is taking place if the running smoothness does not change above a defined limited value.
Accordingly, immediately after the start, an ignition is carried out at least in one cylinder at all upper dead centers (OT), a shifting of the ignition point in time taking place at certain upper dead centers, particularly at each second upper dead center, thus all 720_ of crankshaft angle. According to whether the air-fuel mixture is actually ignited at the upper dead center (OT) at which the shift of the ignition point in time is carried out, or at a crankshaft angle shifted by 360_, a reduction of the indicated work in the respective cylinder can be determined.
Such a reduction of the indicated work can be determined by means of a device for detecting smooth running. If an effect in the smooth running can now be detected by the shift of the ignition angle, the shift of the ignition point in time has taken place in the upper dead center in which an ignition of the air-fuel mixture is actually taking place. If, however, the smooth running does not significantly change as the result of the shift of the ignition point in time, the ignition is taking place in the overlapping upper dead center.
Preferably, a retarding of the ignition angle is selected as the ignition angle shift.
Furthermore, for a further protection and checking of the result of the synchronized ignition, it can be attempted to carry out a countercheck such that the shift of the ignition point in time is in each case offset by 360xc2x0. In the case of a correctly functioning ignition time synchronization, a modification of the smooth running must occur, if there previously was no modification of the smooth running or, vice-versa, a normal smooth running must be present if, before the countercheck, the running was very erratic.
As an alternative to the countercheck, the ignition in other cylinders can be tested, preferably corresponding to their firing sequence.
If the ignition upper dead center was detected in its position with respect to the crankshaft, a change to the normal operation with a single-plug ignition can only take place in the ignition upper dead center. In addition, it is advantageous in this connection to also switch over to a fully sequential injection.
On the whole, the present method offers a simple and cost-effective solution for an effective synchronized ignition. In particular, the costs for a camshaft sensor and its attendant peripheral components can be saved without the requirement of doing without a single-plug ignition or an operation in the fully sequential mode.
Also with respect to additional advantages and characteristics, the invention will be described in detail in the following by means of an embodiment and with respect to the attached drawings.